What are the contradictions of taking pentoxifylline and Minoxidil at the same time?

This is a great question. Certainly ORAL minoxidil and ORAL pentoxifylline present a contraindication given the tendency of pentoxifylline to lower blood pressure in oral minoxidil users. As far as TOPICAL minoxidil goes, there have not been any great studies. One must keep in mind topical minoxidil does not lower blood pressure much in most people who use it as a sole therapy. Certainly there is a risk of lowered blood pressure with pentoxifylline  but the risk overall is low. I advise patients in such a situation to speak to their physicians if other options are available (finasteride, laser or surgery). If these are not options (and sometimes are not in a patient who needs pentoxifylline), topical minoxidil can be considered  on case by case basis only. If a decision is made to start, a low dose every second day is usually the starting point. If the pentoxifylline user has cardiovascular disease or severe peripheral vascular disease (a common reason for pentoxifylline in the first place) or is over 65 or is experiencing side effects on pentoxifylline like dizziness, heart palpitations or headaches I would not generally consider topical minoxidil as these can worsen blood pressure and cardiovascular issues in a pentoxifylline user. In summary the use of TOPICAL minoxidil in someone on oral pentoxifylline is not always possible and can only be approached on a case by case basis. If ever started, one must start a low dose (2 % not 5 %) with daily monitoring of blood pressure and close monitoring of side effects. Other options should be considered first.

These two drugs interact and should not be taken together. Effects on blood prressure are one of the side effects of combining these two drugs